1. Field of the Invention
The present invention relates to a construction of hull of a vessel such as a tanker. More particularly, the invention is concerned with a hull having a construction composed of three hemispheres to attain the maximum internal volume with the minimum outer surface area, while attaining a good stability of the vessel.
2. Description of the Prior Art
Nowadays, the size of hulls of vessels such as tankers is becoming large, and various proposals and attempts are made to maximize the transportation of crude oil or liquefied natural gas per voyage. However, it is considered that there is a practical limit of 500,000 tons in the hull size, as far as the conventional hull construction having substantially rectangular cross-section is concerned, for the following reasons.
Namely, the effect or advantage brought about by the increase of the hull size is not so remarkable, considering the increase of the amount of steel material to be used, when the hull size is increased beyond the above-mentioned practical limit. In addition, the increased hull size imposes a problem concerning the mechanical strength of the hull. Furthermore, the increased hull size correspondingly decreases the speed of the vessel. Much more fuel will be consumed for maintaining the desired speed with the increased hull size. Furthermore, as the hull size such as overall length is increased, the levels of stresses caused by various resistance forces such as wave making resistance to impractically increase the deflection of the hull.
From a mathematical point of view, it is clear that a spherical hull shape (hemispherical shape in actual application) offers the maximum internal volume for a given surface area, i.e. for a given consumption of the steel. From this standpoint, the present inventor has worked out a hemispherical hull and conducted a performance test with this hull. As a result, the inventor has found out that a mere hemispherical hull afloat on the water cannot provide satisfactory steering stability nor substantial increase of the speed.
The inventor has made also an investigation on various hull shapes of tanker vessels and crude oil storage floating structures, and found that no further study has been made up to now for adopting the hemispherical shape of the hull.